Wideband filter for direct connection to differential power amplifier

ABSTRACT

A filter device configured to directly connect to a differential power amplifier of a transmit chain circuit. The filter device may include a transformer and a filter configured as a half lattice equivalent topology and having a single-ended output. The filter may be a lattice filter configured as a full lattice topology or a lattice equivalent filter configured as a half lattice equivalent topology. The filter includes a first branch having a first impedance network of one or more first impedance elements and a second branch having a second impedance network of one or more second impedance elements. The single-ended output of the filter device may connect to an antenna switch that is in turn connected to an antenna.

The present description relates in general to wireless communicationsystems, and in particular power amplifier and filter combinations.

BACKGROUND

A power amplifier combined with a frequency filter forms a key buildingblock in wireless communication systems. The transmit chain of such asystem combines a power amplifier with a filter to suppress unwantedspectral frequencies, with optional switches on either side of thefilter, so that a single antenna or single power amplifier canoptionally connect to multiple filters. Many commonly used poweramplifier designs have differential outputs, meaning the signals at theoutput ports are roughly 180 degrees out of phase. Because most switchand antenna implementations are single-ended, and because the mostcommon filter implementations are single-ended ladder structures, theoutput of the power amplifier often connects to a transformer, whichacts as a balun to convert differential (e.g., balanced) signals tosingle-ended (e.g., unbalanced) signals used by switches, filters, andthe antenna. Furthermore, the output impedance of the power amplifier isusually quite low, on the order of a few ohms or tens of ohms. Thisimpedance must be matched to higher impedances, often near 50 ohms tointerface with typical switches, filters, and antennas. The impedanceconversion can be accomplished with a matching network of transmissionlines or discrete inductors and capacitors.

Unfortunately, the transformer balun and impedance matching; circuitsrequired after the power amplifier may attenuate the power amplifieroutput by more than 1 decibel (dB), in addition to the 1.5 to 2 dBlosses incurred by the filter, for a total loss of approximately 2.5 to3 dB between power amplifier and filter output, not counting anyadditional losses from switches. This added power dissipation increasesthe power required for transmitting signals from the antenna, therebyreducing the battery life in portable wireless devices.

BRIEF DESCRIPTION OF THE DRAWINGS

Certain features of the subject technology are set forth in the appendedclaims. However, for purposes of explanation, several embodiments of thesubject technology are set forth in the following figures.

FIG. 1 is a schematic diagram illustrating an example common topologyfor a transmit chain with multiple filters that connect to adifferential power amplifier.

FIG. 2 is a schematic diagram illustrating an example common topologyfor a differential power amplifier connected to a dedicated filter,

FIG. 3 is a schematic diagram illustrating an example differential poweramplifier with a transformer balun, according to aspects of thedisclosure.

FIG. 4 is a schematic diagram illustrating an exploded view of thedifferential power amplifier of FIG. 3 , according to aspects of thedisclosure.

FIG. 5 is a schematic diagram illustrating an example of a latticefilter, according to aspects of the disclosure.

FIG. 6 is a schematic diagram illustrating an example half-ladder filtertopology, according to aspects of the disclosure.

FIG. 7 is a schematic diagram illustrating an example transmit chain,according to aspects of the disclosure.

FIG. 8 is a schematic diagram illustrating an example filter topology,according to aspects of the disclosure.

FIG. 9 is a schematic diagram illustrating an example filter topology,according to aspects of the disclosure.

FIG. 10 is a schematic diagram illustrating a simulation of an examplefilter topology, according to aspects of the disclosure.

FIG. 11 is a schematic diagram illustrating the results of thesimulation of FIG. 10 , according to aspects of the disclosure.

FIG. 12 is a schematic diagram illustrating a simulated PCB transformerlayout, according to aspects of the disclosure.

FIG. 13 is a schematic diagram illustrating the results of thesimulation of FIG. 12 , according to aspects of the disclosure.

FIG. 14 is a schematic diagram illustrating an example filter topology,according to aspects of the disclosure.

FIG. 15 is a schematic diagram illustrating example network topologies,according to aspects of the disclosure.

FIG. 16 is a schematic diagram illustrating an example transformertopology, according to aspects of the disclosure.

FIG. 17 is a schematic diagram illustrating example equivalenttransformer and inductor topologies, according to aspects of thedisclosure.

FIG. 18 is a schematic diagram illustrating example inductor dotorientations, according to aspects of the disclosure.

DETAILED DESCRIPTION

The detailed description set forth below is intended as a description ofvarious configurations of the subject technology and is not intended torepresent the only configurations in which the subject technology may bepracticed. The appended drawings are incorporated herein and constitutepart of the detailed description, which includes specific details forproviding a thorough understanding of the subject technology. However,the subject technology is not limited to the specific details set forthherein and may be practiced without one or more of the specific details.In some instances, structures and components are shown in ablock-diagram form in order to avoid obscuring the concepts of thesubject technology.

In certain applications where a single power amplifier connects to asingle filter that is only used for transmit (e.g., uplink), no switchis necessary between the power amplifier and filter. Rather thanimplementing a balun to convert differential power amplifier output to asingle-ended signal and inserting matching components to raise theimpedance to match the filter input impedance, a filter may be directlyconnected to the differential output of the power amplifier.

One differential filter topology, called a lattice filter, is a bridgecircuit that has both differential inputs and outputs. This filtertopology can be converted to a “hybrid-lattice” or “half-lattice”equivalent circuit using a transformer, typically with equal windings orturns in each transformer section. The transformer allows one or bothports of the filter to have a ground reference, converting to asingle-ended design. By also varying the turns-ratio of the transformer,the impedance conversion ratio can be varied, so that one side of thefilter can have different effective input impedance from the other. Thistopology has the flexibility to accommodate the impedance transformationfunctions and the conversion from differential signals from the poweramplifier to single-ended signals needed for the antenna connection orother switches near the antenna.

Simulation using film bulk acoustic resonators (FBARs) as filteringelements suggest that the insertion loss is much improved by combiningthe balun, impedance conversion, and filtering functions in a singlefilter of this topology, when compared to the common approach ofinserting a single-ended ladder filter after the power amplifier balunand impedance matching elements. A simulated example suggests aninsertion loss of 2 dB for the combined filter, balun, and impedancematching functions, compared to 2.5-3 dB of loss for traditionalmethods. The implementation may also be more area-efficient, as very fewcomponents are needed in its implementation. The area savings and powersavings could prove useful for many years to come as radio frequency(RF) front-end modules continue to shrink in size, and developers ofportable wireless communication devices require lower power consumptionfor longer battery life.

The subject technology proposes solutions for direct connection betweena differential power amplifier and a filter. Here, only a single filterconnects to the power amplifiers, so there is no intervening switch(e.g., band-select switch or transmit-receive switch) between the filerand power amplifier. However, there may be switches at one or moreantennas to connect to other filters and amplifiers, such as transmit(TX) or receive (RX).

According to aspects of the subject technology, a transmit chain circuitdevice is configured to include a differential power amplifier, a filterdevice directly coupled to the differential power amplifier, and anantenna coupled to the filter device. The filter device has asingle-ended output and may include a filter having multiple impedanceelements and a transformer balun.

According to aspects of the subject technology, a filter device isconfigured to directly connect to a differential power amplifier of atransmit chain circuit. The filter device may include a transformer anda lattice equivalent filter configured as a half lattice equivalenttopology and having a single-ended output. The lattice equivalent filterincludes a first branch having a first impedance network of one or morefirst impedance elements and a second branch having a second impedancenetwork of one or more second impedance elements.

According to aspects of the subject technology, a filter device may beconfigured to directly connect to a differential power amplifier of atransmit chain circuit. The filter device may include a transformer anda lattice filter configured as a full lattice topology and having asingle-ended output. The lattice filter includes a matching networkconfigured to provide impedance transformation and a single-endedfilter.

In aspects of the disclosure as discussed above, a lattice filter mayinclude a first branch having a first impedance network of one or morefirst impedance elements and a second branch having a second impedancenetwork of one or more second impedance elements. Further, multiplelattice topologies, containing different impedances in first and secondbranches, can be cascaded within a single filter. For example, two ormore of the filters shown in FIG. 5 may be connected (e.g., cascaded).

FIG. 1 illustrates an example common topology for a transmit chain 20with a differential power amplifier 30. The transmit chain 20 includesthe differential power amplifier 30 and a transformer balun 40 toconvert the differential power amplifier 30 to single-ended. A matchingnetwork 50 (e.g., matching and tuning network) is used to transform lowimpedance to about 50 ohms. The matching network 50 is formed frommultiple impedance elements 55, where each impedance element 55 mayinclude any combination of inductors, capacitors, transmission lines,resonators, crystals, and/or FBARs. A switch 60 (e.g., band selectswitch) couples the matching network 50 to multiple single-ended filters70, which in turn couple to an antenna switch 80, which in turn couplesto an antenna 90. Differential power amplifier 35 and transformer balun45 may be used instead of differential power amplifier 30 andtransformer balun 40. FIG. 1 illustrates one signal path between thedifferential power amplifier 30, 35 and the antenna 90, though many RFfront-end modules have multiple differential power amplifiers 30, 35 andmultiple antennas 90.

While switch 60 is shown in FIG. 1 as a band select switch where asingle multi-band power amplifier 30, 35 can connect to multiple filters70, switch 60 may be any suitable switching configuration between apower amplifier and a filter. For example, a power amplifier (e.g.,differential power amplifier 30, 35) may connect to only a single filter(e.g., filter 70), which is used for both transmit/uplink andreceive/downlink, where the switch 60 may be a transmit-receive (TRX)switch. For example, for a TRX switch the pole may connect to the filter(e.g., filter 70) and the throws may connect to power amplifiers (e.g.,differential power amplifier 30, 35) for transmit or low-noiseamplifiers (LNA) for receive.

FIG. 2 illustrates an example common topology for a transmit chain 25having a differential power amplifier 30, 35 connected to a dedicatedfilter 70. The differential power amplifier 30 and transformer balun 40or the differential power amplifier 35 and transformer balun 45 may becoupled to the same matching network 50 as in the transmit chain 20.However, the matching network 50 is then coupled directly to a singlededicated filter 70. Here, there is no switch 60 because only a singlefilter 70 connects to the differential power amplifier 30, 35 for adedicated uplink path. The single filter 70 is coupled to the antennaswitch 80, which is coupled to the antenna 90.

Additional matching networks 50 may be coupled between the single filter70 and the antenna switch 80 and/or between the antenna switch 80 andthe antenna 90. These additional matching networks 50 may be used forimpedance matching (e.g., to offset capacitive parasitic of the antennaswitch 80) and/or additional filtering (e.g., harmonic traps to removehigh-order harmonics from the differential power amplifier 30, 35output), and may be implemented as any of a pi network, an L network anda T network, for example. While there is no switch 60 between the filterand power amplifier here, there can still be other switches at one ormore antennas 90 to connect to other filters and amplifiers (e.g., TX,RX). Also, though there is no switch 60 and there is only one dedicatedfilter 70, the transformer balun 40, 45, matching network 50 and filtercomponents (e.g., impedance elements 55) add significant dissipativeloss to the signals.

FIGS. 3 and 4 illustrate an example power amplifier 130 and transformer140, according to aspects of the disclosure, where in FIG. 4 a filterarea 172 is disposed between the power amplifier 130 and the transformer140. The filter area 172 represents bringing the filtering further backin a transmit chain (e.g., transmit chain 20, 25), such as before thetransformer 140 as shown in FIG. 4 . In aspects of the disclosure, thetransformer 140 may be incorporated as part of a filter.

Many different filtering topologies, such as lattice filters and theirequivalents, are capable of very wide filtering bandwidths and excellentwideband rejection using very few components compared to commonly usedhalf-ladder topologies. For example, a lattice filter 174 is shown inFIG. 5 and is formed from multiple impedance elements 55. Lattice filter174 is suitable for balanced/differential connections. As shown in FIG.6 , a half ladder 176 is also formed from multiple impedance elements55. Half ladder 176 is suitable for unbalanced, single-ended connections

FIG. 7 shows an example transmit chain 120 that incorporates thisconcept of bringing the filtering back in the chain between thedifferential power amplifier 30 and the transformer balun 40 fromtransmit chain 20 shown in FIG. 1 , Transmit chain 120 allows for adirect connection between the differential power amplifier 30 and thefilter 174. The filtering is shown as a lattice filter 174 representinga full lattice topology, but other filtering topologies that supportdifferential input and output signals are possible. The transmit chain120 also includes the antenna switch 80 and the antenna 90 from transmitchain 20. Here, there is no switch 60 because only a single filter 174connects to the differential power amplifier 30. There may be switchesat one or more antennas 90 to connect to other filters and amplifiers(e.g., TX, RX), In addition, the boxed area shown in FIG. 7 combines thefunctions of the filter 70, the transformer balun 40 and the matchingnetwork 50 (e.g., impedance conversion) from the transit chain 20. Inaspects of the disclosure, the antenna switch 80 may be omitted and theantenna 90 coupled to the output of the boxed area.

In aspects of the disclosure, the filtering may be transformed intoother equivalents, such as a half-lattice or hybrid lattice as shown inFIG. 8 . For example, the full lattice topology of lattice filter 174may be replaced by a half lattice equivalent network 177. The latticefilter 174 and the half lattice equivalent network 177 have differentialinput and output signals, which require identical port impedances due tosymmetry. However, the half lattice equivalent network 177 may betransformed from a differential port to single-ended to yield filter178. Here, isolating the transformer allows the application of a groundreference 173 for the single-ended connection 171. Thus, filter 178 isnot burdened in the same manner as lattice filter 174 or half latticeequivalent network 177 regarding the output signals.

Impedance transformation is possible with an n=1 turns ratio withappropriately chosen impedance values for Za and Zb. In aspects of thedisclosure, an addition of arbitrary turns ratio n adjustments providesfor adjustable filter 179, as shown in FIG. 8 . For adjustable filter179, arbitrary turns ratio n and adjustments to impedance elements 55(e.g., impedance blocks) helps filter to transform impedance levels.Thus, the arbitrary turns ratio n adds degrees of freedom for impedancetransformation or optimization of the filter performance. In aspects ofthe disclosure, adjustable filter 179 has the flexibility to performdifferential to single-ended conversion, and impedance transformationtoo, by varying the impedance elements 55 and transformer 140transformation turns ratio n. Impedance elements 55 are networkscontaining any combination of inductors, capacitors, resistors,transmission lines, crystals, or resonators. Thus, the changes tocombine filtering, balun and impedance conversion functions allows forconnecting directly to differential power amplifier 30, 35.

FIG. 9 illustrates an example filter 270 having a half-latticeequivalent 177 with a center-tapped transformer 240, where awell-designed transformer 240 offers common-mode rejection. For example,additional external matching components 242 may be used to obtain thedesired transformer 240. Filter 270 includes two impedance elements 255,each impedance element 255 having two FBAR resonators 256 and oneinductor 258. In aspects of the disclosure, impedance element 255 may beany combination of inductors, capacitors, resistors, crystals, orresonators. As shown, filter 270 may be directly coupled to differentialpower amplifier 30. In aspects of the disclosure, filter 270 may bedirectly coupled to differential power amplifier 35 or any othersuitable differential power amplifier.

FIG. 10 shows a simulation example of a filter 370 (e.g., N77 filter)using an ideal center-tapped transformer. Here, differential portsconnect directly to a differential power amplifier (e.g., differentialpower amplifier 30, 35) having differential impedance of 17+5*j ohms. Onthe other end, a single-ended port connects to an antenna (e.g., antenna90) or antenna switches (e.g., antenna switch 80). For this simulation,the FBAR modified Butterworth-Van Dyke (MBVD) model loss assumptions areRO=0.3, Rm=0.5, Rs=0.8, Rp50˜4000 ohms, Rs50˜1.1 ohms, and an Ohm/nHlosses for all printed circuit board (PCB) inductors.

FIG. 11 shows the results of the simulation using example filter 370with an ideal center-tapped transformer of FIG. 10 . Here, the idealtransformer is assumed to have perfectly matched phases and the shadedboxes indicate where rejection is needed.

FIG. 12 shows a simulation example using a simulated. PCB transformer440 layout (e.g., non-ideal transformer) having secondary ports 441 andprimary ports 443. Here, the PCB layout area 442 for the transformer 440used in the filter (e.g., filter 370) is comparable to typicaltransformer baluns (e.g. transformer balun 40) used at the output of thedifferential power amplifier. A simulation model 444 includes surfaceroughness losses. A resulting SSP file 446 is used as an SSP block in acircuit simulation 448, As shown in the circuit simulation 448, the FBARfiltering, which is based on an efficient lattice implementation isquite area-efficient, requiring only a few resonators.

FIG. 13 shows a simulation example of filter 370 reoptimized with thesimulated PCB transformer 440 of FIG. 12 . The filter design, using thisnon-ideal transformer 440, which is more realistic in application thanthe ideal transformer of FIG. 10 , has phase and amplitude that are nolonger perfectly balanced (e.g., + or −5 degrees), yet still able to geta good degree of rejection. This not perfectly balanced transformer 440may be suitable if the layout is symmetric and process variations arewell-controlled. In the simulation, the insertion loss is good (e.g., 2dB) based on combining multiple functions in one block.

In aspects of the disclosure, there are several possible impedanceelements for a filter, such as filter 570 shown in FIG. 14 . Here, theimpedances Zx and Zy in each branch determine the frequency response ofthe filter 570, For example, depending on the phase responses of theimpedances Zx and Zy, the structure can implement bandpass, bandstop,low-pass, or high-pass filtering functions within a given frequencyrange. Also, the impedances Zx and Zy may include any networkcombination of elements. For example, reactive elements such asinductors and capacitors, or dissipative elements such as resistors,which may be implemented on PCB, integrated passive device (IPD),integrated circuit (IC) process, low-temperature co-fired ceramic (LTCC)substrates, or discrete components, such as surface-mount devices (SMD).Combinations of the above components may be used to create resonantstructures.

As another example, combinations of electromechanical or acousticresonators may be used. These may include bulk-acoustic wave (BAW)resonators, FBAR, surface acoustic wave (SAW) resonators, or crystalsthat have been cut to function as resonators (crystal resonators). Forbetter power-handling or reduction or to suppress second-ordernon-linearities, resonators may be connected in parallel (e.g.,split-bar) or in series (e.g., power-bar) forms. In yet another example,active circuitry may be used, such as transistors or amplifiers combinedwith passive elements to create impedances with the desired impedanceand phase response for the filter 570.

If the impedances Zx and Zy share a common impedance Zc connected inseries (or shunt) position, that component can be moved to the externalterminals in a series (or shunt) position with appropriate impedancescaling factors. As an example, equivalent networks 572, 574, 576 areshown in FIG. 15 for a common series impedance Zc and a filterimplementation with n=1. When a non-ideal transformer is used (e.g.,coupling coefficient k<1), when n≠1, or when parasitic elements areincluded, the scaling factors for the common impedance Zc will bedifferent than shown in FIG. 15 , or the network may not be exactlyequivalent, but a similar concept still applies.

In aspects of the disclosure, implementation of the impedance Zc may bemore convenient outside of Zx and Zy branches due to fabricationprocesses, or the impedance might be implemented with lower lossesoutside of the Zx and Zy branches. For example, in the filter designsshown in FIGS. 9-11 , the inductance La1 could be removed from onebranch (and also subtracted from La3 in the other branch), to bereplaced as scaled inductors at the input and outputs of the filter. Thenetworks 572, 574, 576 may be incorporated into any of theabove-discussed implementations if allowing for arbitrary Zx and Zynetworks and recognizing that additional electrical components can becascaded at the input and output of the filter.

In aspects of the disclosure, there are several potentialimplementations of a center-tapped transformer 540, as shown in FIG. 16. The transformer 540 is effectively three inductors with coupledmagnetic flux, as shown in FIG. 17 in the equivalent center-tappedtransformer network 542 and mutually coupled inductor network 544, andmay be implemented as such. For example, sufficient filter behavior maybe obtained when turns ratios (e.g., n2 and n3) of the center-tappedtransformer 542 or inductors Lx2 and Lx3 of mutually coupled inductornetwork 544 are not identical in value (e.g., the self inductances andthe mutual inductances among the three inductors have different values).Simulation and optimization yield reasonable filter responses when Lx2and Lx3 inductances (or ratios n2 and n3) are mismatched by a fewpercent, such as in a practical implementation where there is usuallysome mismatch. Likewise, the mutual coupling coefficient (e.g., kxfm)need not be ideal (e.g., near 1) or identical for the three inductorsthat comprise the transformer, as adjustments to Zx and Zy impedancescan compensate for mismatch to still obtain reasonable filter responses.For example, the simulated PCB implementation of FIGS. 12 and 13 has anestimated coupling k˜0.5, suggesting some flux leakage.

As shown in FIG. 18 , the orientations (e.g., dot notation) 546 of theinductor windings may be flipped in certain ways. For example, theorientation of the Lx1 inductor does not matter and either terminal canserve as GND reference on the left port. Also, Lx2 & Lx3 can be flipped,as long as both are flipped together. Each of the examples shown in FIG.17 are acceptable inductor orientations using mutually coupled inductor“dot” notation 546.

Implementations within the scope of the present disclosure can bepartially or entirely realized using a tangible computer-readablestorage medium (or multiple tangible computer-readable storage media ofone or more types) encoding one or more instructions. The tangiblecomputer-readable storage medium also can be non-transitory in nature.

The computer-readable storage medium can be any storage medium that canbe read, written, or otherwise accessed by a general-purpose orspecial-purpose computing device, including any processing electronicsand/or processing circuitry capable of executing instructions. Forexample, without limitation, the computer-readable medium can includeany volatile semiconductor memory, such as RAM, DRAM, SRAM, T-RAM, Z-RAMand TTRAM. The computer-readable medium also can include anynon-volatile semiconductor memory, such as ROM, PROM, EPROM, EEPROM,NVRAM, flash, nvSRAM, FeRAM, FeTRAM, MRAM, PRAM, CBRAM, SONGS, RRAM,NRAM, racetrack memory, FJG and Millipede memory.

Further, the computer-readable storage medium can include anynon-semiconductor memory, such as optical disk storage, magnetic diskstorage, magnetic tape, other magnetic storage devices, or any othermedium capable of storing one or more instructions. In someimplementations, the tangible computer-readable storage medium can bedirectly coupled to a computing device while, in other implementations,the tangible computer-readable storage medium can be indirectly coupledto a computing device, e.g., via one or more wired connections, one ormore wireless connections, or any combination thereof.

Instructions can be directly executable or can be used to developexecutable instructions. For example, instructions can be realized asexecutable or non-executable machine code or as instructions in ahigh-level language that can be compiled to produce executable ornon-executable machine code. Further, instructions also can be realizedas or can include data. Computer-executable instructions also can beorganized in any format, including routines, subroutines, programs, datastructures, objects, modules, applications, applets, functions, etc. Asrecognized by those of skill in the art, details including, but notlimited to, the number, structure, sequence and organization ofinstructions can vary significantly without varying the underlyinglogic, function, processing and output.

While the above discussion primarily refers to microprocessor ormulticore processors that execute software, one or more implementationsare performed by one or more integrated circuits, such asapplication-specific integrated circuits (ASICs) or field-programmablegate arrays (FPGAs). In one or more implementations, such integratedcircuits execute instructions that are stored on the circuit itself.

The previous description is provided to enable any person skilled in theart to practice the various aspects described herein. Variousmodifications to these aspects will be readily apparent to those skilledin the art, and the generic principles defined herein may be applied toother aspects. Thus, the claims are not intended to be limited to theaspects shown herein, but are to be accorded the full scope consistentwith the language claims, wherein reference to an element in thesingular is not intended to mean “one and only one” unless specificallyso stated, but rather “one or more.” Unless specifically statedotherwise, the term “some” refers to one or more. Pronouns in themasculine (e.g., his) include the feminine and neuter gender (e.g., herand its) and vice versa. Headings and subheadings, if any, are used forconvenience only and do not limit the subject disclosure.

The predicate words “configured to,” “operable to,” and “programmed to”do not imply any particular tangible or intangible modification of asubject, but rather are intended to be used interchangeably. Forexample, a processor configured to monitor and control an operation or acomponent may also mean the processor being programmed to monitor andcontrol the operation or the processor being operable to monitor andcontrol the operation. Likewise, a processor configured to execute codecan be construed as a processor programmed to execute code or operableto execute code.

A phrase such as “an aspect” does not imply that such aspect isessential to the subject technology or that such aspect applies to allconfigurations of the subject technology. A disclosure relating to anaspect may apply to all configurations or one or more configurations. Aphrase such as “an aspect” may refer to one or more aspects and viceversa. A phrase such as “a configuration” does not imply that suchconfiguration is essential to the subject technology or that suchconfiguration applies to all configurations of the subject technology. Adisclosure relating to a configuration may apply to all configurations,or one or more configurations. A phrase such as a configuration mayrefer to one or more configurations and vice versa.

The word “example” is used herein to mean “serving as an example orillustration.” Any aspect or design described herein as “an example” isnot necessarily to be construed as preferred or advantageous over otheraspects or designs.

All structural and functional equivalents to the elements of the variousaspects described throughout this disclosure that are known or latercome to be known to those of ordinary skill in the art are expresslyincorporated herein by reference and are intended to be encompassed bythe claims. Moreover, nothing disclosed herein is intended to bededicated to the public regardless of whether such disclosure isexplicitly recited in the claims. No claim element is to be construedunder the provisions of 35 U.S.C. § 112, sixth paragraph, unless theelement is expressly recited using the phrase “means for” or, in thecase of a method claim, the element is recited using the phrase “stepfor.” Furthermore, to the extent that the terms “include,” “have,” orthe like are used in the description or the claims, such terms areintended to be inclusive in a manner similar to the term “comprise,” as“comprise” is interpreted when employed as a transitional word in aclaim.

Those of skill in the art would appreciate that the various illustrativeblocks, modules, elements, components, methods and algorithms describedherein may be implemented as electronic hardware, computer software, orcombinations of both. To illustrate this interchangeability of hardwareand software, various illustrative blocks, modules, elements,components, methods and algorithms have been described above generallyin terms of their functionality. Whether such functionality isimplemented as hardware or software depends upon the particularapplication and design constraints imposed on the overall system.Skilled artisans may implement the described functionality in varyingways for each particular application. Various components and blocks maybe arranged differently (e.g., arranged in a different order, orpartitioned in a different way), all without departing from the scope ofthe subject technology.

What is claimed is:
 1. A transmit chain circuit device comprising: adifferential power amplifier; a filter device directly coupled to thedifferential power amplifier and having a single-ended output, thefilter device configured as a half lattice equivalent networkcomprising: a plurality of impedance elements; and a transformer balun;and an antenna coupled to the filter device, wherein the filter deviceis configured to transform impedance levels based on a turns ratio ofthe transformer balun and the plurality of impedance elements.
 2. Thetransmit chain circuit device of claim 1, further comprising an antennaswitch coupled to the filter device and to the antenna.
 3. The transmitchain circuit device of claim 1, wherein the turns ratio is
 1. 4. Thetransmit chain circuit device of claim 1, wherein the turns ratio isarbitrary.
 5. The transmit chain circuit device of claim 1, wherein oneor more of the plurality of impedance elements comprise a resonantstructure formed from a combination of any of inductors, capacitors andresistors.
 6. The transmit chain circuit device of claim 1, wherein oneor more of the plurality of impedance elements comprise a combination ofresonators formed from any of bulk-acoustic wave resonators, film bulkacoustic resonators, surface acoustic wave resonators and crystalresonators.
 7. The transmit chain circuit device of claim 1, wherein oneor more of the plurality of impedance elements comprise a combination ofany of transistors and amplifiers with passive elements.
 8. The transmitchain circuit device of claim 1, wherein the filter device comprises: afirst branch having a first impedance element network; and a secondbranch having a second impedance element network, wherein the first andsecond impedance element networks each have a common impedance elementconnected in series, and wherein the common impedance elements arecoupled to external terminals in a series position with impedancescaling factors.
 9. The transmit chain circuit device of claim 1,wherein the transformer balun comprises a center-tapped transformer, andwherein two turns ratios of the center-tapped transformer have differentvalues.
 10. The transmit chain circuit device of claim 1, wherein thetransformer balun comprises a mutually coupled inductor networkcomprising three inductors with coupled magnetic flux, and wherein theself inductances and the mutual inductances among the three inductorshave different values.
 11. A filter device for a transmit chain circuit,the filter device comprising: a transformer; and a plurality ofimpedance elements, wherein the filter device is configured as a halflattice equivalent network having a single-ended output, the halflattice equivalent network comprising: a first branch having a firstimpedance network of one or more first impedance elements of theplurality of impedance elements; and a second branch having a secondimpedance network of one or more second impedance elements of theplurality of impedance elements, wherein: the filter device isconfigured to directly couple to a differential power amplifier, and thefirst and second impedance networks each have a common impedance elementconnected in series, and wherein the common impedance element is coupledto external terminals in a series position with impedance scalingfactors.
 12. The filter device of claim 11, wherein each of the firstand second branches has an arbitrary turns ratio, and wherein the filterdevice is configured to transform impedance levels based on thearbitrary turns ratio and adjustments to the first and second impedancenetworks.
 13. The filter device of claim 11, wherein the transformercomprises a center-tapped transformer, and wherein first and secondturns ratios of the center-tapped transformer have different values. 14.The filter device of claim 11, wherein the transformer comprises amutually coupled inductor network comprising three inductors withcoupled magnetic flux, and wherein the self inductances and the mutualinductances among the three inductors have different values.